Method for operating a burner and burner with stepped premix gas injection

ABSTRACT

The present invention relates to a method of operating a burner, which comprises at least one first fuel supply conduit ( 5 ) with a first group of fuel outlet openings ( 6 ), essentially arranged in the direction of a burner longitudinal axis ( 3 ), for a first premix fuel quantity and one or a plurality of second-fuel supply conduits ( 7 ) with a second group of fuel outlet openings ( 8 ), essentially arranged in the direction of the burner longitudinal axis ( 3 ), for a second premix fuel quantity, it being possible to admit fuel to the second fuel supply conduits ( 7 ) independently of the first fuel supply conduit ( 5 ). In the method, both fuel supply conduits ( 5, 7 ) are operated with the same fuel. By means of the present method of operating a burner, optimum mixing conditions can be set even in the case of different loads, gas qualities or gas preheat temperatures.

TECHNICAL FIELD OF APPLICATION

[0001] The present invention relates to a method of operating a burner,which has at least one first fuel supply conduit with a first group offuel outlet openings, essentially arranged in the direction of a burnerlongitudinal axis, for the introduction of a first premix fuel quantityinto a swirl space and one or a plurality of second fuel supply conduitswith a second group of fuel outlet openings essentially arranged in thedirection of the burnerlongitudinal axis, it being possible to admitfuel to the second fuel supply conduits independently of the first fuelsupply conduit. The invention also relates to a burner which can beadvantageously operated by means of the method. The combustion spaces ofgas turbines are a preferred field of employment for such burners; inaddition such burners are, for example, also employed in atmosphericboiler firing systems.

PRIOR ART

[0002] A conical burner consisting of a plurality of shells, a so-calleddouble-cone burner as described in the preamble to claim 1, is knownfrom EP 0 321 809. A swirl flow in the interior space of the coneenclosed by the conical partial shells is generated by the conical swirlgenerator composed of a plurality of shells. Because of across-sectional step at a combustion-space end of the burner, the swirlflow becomes unstable and merges into an annular swirl flow with reverseflow at the core. This reverse flow permits stabilization of a flamefront at the burner outlet. The shells of the swirl generator arecombined in such a way that tangential air inlet slots for combustionair are formed along the burner longitudinal axis. Supply conduits for agaseous premix fuel are provided at the inlet flow edge of the conicalshells formed by this means. These supply conduits have outlet openings,distributed in the direction of the burner longitudinal axis, for thepremix gas. The gas is injected transverse to the air inlet gap throughthe outlet openings or holes. In association with the swirl, generatedin the swirl space, of the flow of combustion air and fuel gas flow,this injection leads to good mixing of the fuel gas or premix gas withthe combustion air. In such premix burners, good mixing is theprecondition for low NO_(x) values during the combustion process.

[0003] For further improvement to such a burner, a burner for a heatgenerator is known from EP 0 780 629, which burner has an additionalmixing section, which abuts the swirl generator, for further mixing offuel and combustion air. This mixing section can, for example, beembodied as a downstream tube, into which the flow emerging from theswirl generator is transferred without appreciable flow losses. By meansof this additional mixing section, the degree of mixing can be furtherincreased and, therefore, the pollutant emissions reduced.

[0004] WO 93/17279 shows a further known premix burner, in which acylindrical swirl generator with an additional conical inner body isemployed. In this burner, the premix gas is likewise injected into theswirl space by means of supply conduits with corresponding outletopenings, which are arranged along the axially extending air inletslots. In the conical inner body, this burner has, in addition, acentral supply conduit for fuel gas, which can be injected for pilotoperation into the swirl space near the outlet opening of the burner.This additional pilot stage is used for starting the burner. The supplyof the pilot gas in the outlet region of the burner leads, however, toincreased NO_(x) emissions because it is only inadequate mixing with thecombustion air which can take place in this region.

[0005] EP 0918191 A1 shows a burner, of the generic type, for operatinga heat generator which, parallel to a first supply conduit for fuel,also has a second supply conduit for another type of fuel, which supplyconduit is matched to the other type of fuel. The two supply conduitscan be initiated independently of one another. By means of this design,the burner can be operated, without modification, on different types offuel.

[0006] In all the burners presented, the injection of the premix gas inthe air inlet gap takes place by means of supply conduits with outletopenings essentially arranged in the direction of the burnerlongitudinal axis. In consequence, the characteristics of the injectionare predetermined with respect to penetration depth, mixing of the gasjets and the fuel distribution along the air inlet slots or the burnerlongitudinal axis. The arrangement of the outlet openings has thereforealready determined the quality of mixing of the gas and the combustionair and the fuel distribution at the burner outlet. These parametersare, in turn, decisive for the NO_(x) emissions, for the flame-out andflash-back limits and for the stability of the burner with respect tocombustion pulsations.

[0007] In the case of different loads, gas qualities or gas preheattemperatures, however, different upstream gas pressures occur at theoutlet openings and these, in turn, lead to different premixingconditions and mixture qualities at the fuel outlet. The differentpremixing conditions then result in different emission values andstability conditions, which depend on the load, the gas quality and thegas preheating. The known burners can therefore only be operatedoptimally for quite specific value ranges of these parameters.

[0008] A problematic feature in the operation of premix burners,particularly in gas turbines, is the part-load range because, in thisrange, the combustion air is mixed with only comparatively small fuelquantities. In the case of the complete mixing of the fuel with thewhole of the air, however, a mixture occurs which is no longer capableof being ignited, particularly in the lower part-load range, or is onlycapable of forming a very unstable flame. This can lead to damagingcombustion pulsations or to the flame becoming completely extinguished.

[0009] In order to match the known burners to certain emission values orto a certain stability window in the case of different loads,environmental conditions, gas qualities and preheat temperatures, thepossibility currently exists of, on the one hand, staging the premix gassupply to individual burner groups in cases where multiple burnerarrangements are employed. This, however, is only possible in the caseof multi-row burner arrangements. In the case of single-row annularcombustion chambers, this technology has the disadvantage that atemperature profile, which is non-uniform in the peripheral direction,appears at the combustion chamber outlet.

[0010] Another possibility, as already sketched above, is to equipburners with a so-called pilot fuel supply. The burners are thenoperated as diffusion burners at very high excess air numbers. Thisresults, on the one hand, in superior flame stability but, on the other,in high emission values and further technical disadvantages inoperation.

[0011] The object of the present invention consists in providing aburner operating method and a burner, by means of which the burner can,as far as possible, be stably operated in premix operation atapproximately constant NO_(x) emission values, even in the case ofchanges to the load, the gas quality or the gas preheat temperature.

PRESENTATION OF THE INVENTION

[0012] The object is achieved by means of the method according to claims1 and 7 and the burner according to claim 8. Advantageous designs anddevelopments of the burner and the method are the subject matter of thesubclaims.

[0013] In the present method, a burner with swirl body and swirl spaceis employed which has at least one first fuel supply conduit, with afirst group of fuel outlet openings essentially arranged in thedirection of a burner longitudinal axis, for the introduction of a firstpremix fuel quantity into the swirl space and one or a plurality ofsecond fuel supply conduits with a second group of fuel outlet openingsessentially arranged in the direction of the burner longitudinal axis,it being possible to admit fuel to the second fuel supply conduitsindependently of the first fuel supply conduit. In order to operate theburner, the supply of the fuel via the first fuel supply conduits iscontrolled, in an open-chain or closed-loop manner, separately from thesupply of the fuel via the second fuel supply conduits, the same fuelbeing supplied to the first and second fuel supply conduits. Bycontrolling the mass flow ratio between the first fuel quantity suppliedvia the first fuel supply conduits and a fuel quantity supplied via thesecond fuel supply conduits during the operation of the burner, theburner can be stably operated with approximately constant NO_(x),emission values even in the case of changes to the load, the gas qualityor the gas preheat temperature.

[0014] In the preferred embodiment, the fuel is then employed as apremix fuel and is divided at variable mass flow ratio between the firstand second supply conduits. The feed of premix fuel differs from thefeed of pilot fuel, i.e. of fuel for realizing a pilot stage, in thatpremix fuel is introduced into the swirl space with a higher inertia,preferably transverse to the flow of the combustion air. When, on theother hand, the fuel is introduced as pilot fuel, the burner is operatedin a diffusion mode.

[0015] The fuel is preferably introduced into the burner in such a waythat it is distributed between the first and second fuel supply conduitsas a function of the load.

[0016] In a further preferred mode of operation of the burner, in afirst operating condition, the whole of the fuel quantity is essentiallysupplied via the first fuel supply conduit or conduits and is introducedinto the combustion airflow via the first group of fuel outlet openingsand, in a further operating condition, at least a part of the total fuelquantity is introduced into the combustion airflow via at least one ofthe second fuel supply conduits with the second group of fuel outletopenings.

[0017] If the burner is operated in a heat generator, the total fuelcan, in a partial load condition of the heat generator, be supplied viathe first fuel conduits and, in full-load operation of the heatgenerator, the fuel can be divided between the first fuel supplyconduits and one or a plurality of second fuel supply conduits.

[0018] In addition to the above-mentioned load-dependent distribution ofthe fuel between the first and second fuel supply conduits, thedistribution can also be controlled according to other operatingparameters. As an example, the fuel can also be distributed between thefirst and second fuel supply conduits as a function of measuredcombustion chamber pulsations of a gas turbine, of pollutant emissions,of measured material temperatures, of the flame position recorded by aflame position sensor or of other measured or operating parameters.

[0019] The one or a plurality of second fuel supply conduits, by meansof which the quantity—and therefore also the upstream fuel pressure—ofpremix fuel which is injected into the swirl space via the second groupof fuel outlet openings can be set independently of the quantity ofpremix fuel which flows via the first fuel supply conduits, makepossible a simple matching of the mixture distribution and the mixturequality to different boundary conditions. In addition, this design alsomakes it possible to achieve compensation for different Wobbe indicesby, for example, the first fuel supply conduits supporting a certainpower or a certain volume flow and the rest of the power or the volumeflow being operated by means of the second fuel supply conduits. Theaxial and radial fuel distribution in the burner can be favorablyinfluenced by appropriate arrangement of the second fuel supplyconduits, with the corresponding second group of fuel outlet openings,relative to the first fuel supply conduits, with the first group of fueloutlet openings. It is therefore possible to achieve a specifiedenrichment of the mixture with fuel in certain regions of the burneroutlet, during part-load operation, in order to improve the flamestability. At high burner load, the fuel can then be uniformlydistributed, which results in low emissions.

[0020] By means of a design, in which premix fuel can also beadmitted—and is admitted—to a plurality of second fuel supply conduitsindependently of one another, an even more finely staged matching of themixture distribution and the mixture quality to different boundaryconditions can be undertaken.

[0021] In addition, the invention also includes designs such as those inwhich—in addition to first and second fuel supply conduits—third, fourthetc fuel supply conduits are also present and can have fuel admitted tothem independently.

[0022] The present burner consists of a swirl generator for a combustionairflow, a swirl space and means for introducing fuel into thecombustion airflow, the swirl generator having combustion air inletopenings for the combustion airflow entering tangentially into the swirlspace, which comprise means for introducing fuel into the combustionairflow of one or a plurality of first fuel supply conduits with a firstgroup of fuel outlet openings, essentially arranged in the direction ofa burner longitudinal axis, for a first premix fuel quantity and theburner has one or a plurality of second fuel supply conduits with asecond group of fuel outlet openings essentially arranged in thedirection of the burner longitudinal axis, for a second fuel quantity,preferably a premix fuel quantity, it being possible to admit fuel tothese second fuel supply conduits independently of the first fuel supplyconduit or conduits. In the preferred variant described, the burner ischaracterized by an inner body being arranged in the swirl space, thefuel outlet openings of at least one second fuel supply conduit beingarranged on the inner body, essentially distributed in the direction ofthe burner longitudinal axis. In a preferred embodiment, the inner bodyis a fuel lance, which is arranged in the swirl space on the burnerlongitudinal axis.

[0023] One or a plurality of the first groups of fuel outlet openingsare preferably arranged in the region of at least one of the combustionair inlet openings.

[0024] In the present application, an arrangement essentially in thedirection of the burner longitudinal axis is to be understood as anarrangement on longitudinal axiss which extend parallel to or at anangle of <45° to the burner longitudinal axis.

[0025] In a possible embodiment of the present burner, some of thesecond fuel supply conduits are also arranged immediately adjacent tothe first fuel supply conduits, preferably parallel to the latter. Inthis arrangement, at least one second fuel supply conduit should beprovided adjacent to each first fuel supply conduit.

[0026] It is, however, obvious per se that the second fuel supplyconduits can also be provided in symmetrical arrangement on the swirlgenerator, independently of the first fuel supply conduits. In thiscase, the geometry of the swirl generator is unimportant. As an example,conical swirl generators, such as are known from the publications,mentioned at the beginning, of the prior art, for example with two, fouror more air inlet slots, can be employed. Other geometries, such ascylindrical swirl generators or cylindrical swirl generators withconical or cylindrical inner bodies can also be employed.

[0027] In one embodiment of the burner, some of the second fuel supplyconduits are arranged on the outer shell of the swirl body and inparticular, in this arrangement, on the air inlet slots along thelatter. In the present burner, the essential feature is that the secondfuel supply conduits have a plurality of fuel outlet openings, which areessentially distributed in the direction of the burner longitudinalaxis, in order to permit the achievement of adequate premixing. Theoutlet openings are usually located on longitudinal axiss extendingparallel to the burner longitudinal axis or on longitudinal axis at anangle to the burner longitudinal axis predetermined by a conical shapeof the swirl generator or inner body.

[0028] Depending on the possibilities desired for influencing thepremixing, the second fuel outlet openings of the second fuel supplyconduits can have different distances between them or flow crosssections, as compared with the first fuel outlet openings. Particularlyin the case of an arrangement in which at least one second fuel supplyconduit is also provided immediately adjacent to a first fuel supplyconduit, the respective fuel outlet openings can also have the samedistances between them, but be arranged offset relative to one another.This leads to a uniform injection of the premix fuel into the swirlspace. In addition, the first fuel outlet openings can, for example, bearranged over the whole of the axial extent of the combustion air inletopenings, but the second fuel outlet openings being only arranged withina certain partial axial region. In a similar manner, it is also possibleto provide the first fuel outlet openings in a first axial partialregion only and the second fuel outlet openings only in a second axialpartial region abutting the first partial region—or vice versa.Different possibilities for influencing the operation of the burner onthe basis of these different design possibilities, to whose combinationno practical limits are set, can be taken from the exemplaryembodiments.

[0029] For mutually independent admission of the premix fuel to thefirst and the second fuel supply conduits, the latter are equipped withdifferent connections. Additional means are preferably provided for themutually independent closed-loop or open-chain control of the premixfuel supply to the first and the second fuel supply conduits. Thedifferent supply can, for example, be controlled by an suitable controlvalve.

[0030] The burner [sic] according to the invention and burner, by meansof which the method according to the invention can be carried out, areagain explained in more detail below using exemplary embodiments inassociation with the drawings, without limitation to the general conceptof the invention. In the drawings:

[0031]FIG. 1 shows, diagrammatically, an exemplary embodiment of aburner which can be operated with the method according to the invention,in longitudinal and transverse cross section;

[0032]FIG. 2 shows an example of the gas outlet from the outlet openingsin a possible mode of operation of the burner represented in FIG. 1;

[0033]FIG. 3 shows, diagrammatically, an example of the arrangement ofthe fuel supply conduits and the burner outlet openings of a burnerwhich can be operated with the method according to [lacuna] theinvention;

[0034] FIGS. 5 to 7 show examples of the arrangement of the fuel supplyconduits and fuel outlet openings of a burner which can be operated withthe method according to the invention;

[0035]FIG. 8 shows, diagrammatically, an example of a burner with acylindrical swirl generator which can be operated with the methodaccording to the invention;

[0036]FIG. 9 shows an example of a burner construction with cylindricalswirl body and conical inner body, such as can be operated with themethod according to the invention;

[0037]FIG. 10 shows a first example of the design of a burner accordingto the invention;

[0038] FIGS. 11 to 14 show, diagrammatically, examples of further swirlgenerator geometries by means of which the present invention can beeffected;

[0039]FIGS. 15 and 16 show swirl generator geometries with a downstreampremixing tube, by means of which the invention can be effected;

[0040]FIGS. 17 and 18 show, diagrammatically, examples of theconstruction of the swirl body in cross section, such as can be employedin the burner according to the invention;

[0041] FIGS. 19 to 21 show further examples of the design of a burneraccording to the invention;

[0042]FIG. 22 shows an example of the mode of operation of a burner fromFIGS. 20 and 21; and

[0043]FIGS. 23 and 24 show, diagrammatically, two examples of the designof the fuel supply conduits for carrying out the method according to theinvention.

WAYS OF CARRYING OUT THE INVENTION

[0044] The following figures show the burners in strongly diagrammaticembodiment, so that only the features essential for the respectiveexplanation are emphasized in each case. The specialist is familiar withthe further arrangement of the burners represented, inter alia from thedocuments cited as the prior art, which represent an integratedconstituent of the present description. In addition, reference is madein some cases to the injection of gaseous fuel in the exemplaryembodiments. It is, however, obvious per se that liquid fuels can alsobe introduced into the combustion air flow via the fuel outlet openings.The fuel is, in addition, referred to as premix fuel; it is obvious perse that a part of the total fuel quantity can also be introduced incertain load ranges as pilot fuel in order to further increase the flamestability. No supply conduits for pilot fuel are shown in any of thefigures because they are not essential to the invention; given knowledgeof the prior art, the specialist will, however, readily know how toimplement these in the burners represented as examples, should heconsider this to be necessary.

[0045] A first example of a burner which can be operated with the methodaccording to the invention is represented in FIG. 1. FIG. 1a shows anarrangement of the first fuel supply conduit 5 and the second fuelsupply conduit 7 in the case of a burner with conical swirl body 1. Inthe outer shell of this swirl body 1, a second supply conduit 7 for asecond premix fuel quantity P2 is arranged adjacent to the first supplyconduit 5 for a first premix fuel quantity P1 in the outer shell of thisswirl body 1 on the inlet flow edges of the air inlet slots, as they areknown to the specialist from the prior art. Premix fuel can be admittedto these two supply conduits independently of one another, i.e. the massflow of the second premix fuel P2, which flows through the second supplyconduit 7, for example, can be set independently of the mass flow of thefirst premix fuel P1 through the first supply conduit 5. This isindicated by the arrows through the different supply conduits. It isobvious per se that a plurality of these supply pairs 5, 7 arepreferentially arranged symmetrically around the burner longitudinalaxis. The fuel supply to the two supply ducts can be set, independentlyof one another, by means of control valves which are not explicitlyshown here. The arrangement of the control valves is not represented inthe example but the specialist is readily familiar with it.

[0046] The burner is represented in the vertical section through theburner longitudinal axis 3 in FIG. 1b. In this illustration, the twoshells 1 a, 1 b of the swirl body can be recognized. These are arrangedwith axes of symmetry 3 a, 3 b offset to the actual burner longitudinalaxis 3 in such a way that air inlet slots 4 for the combustion air 11are configured between them. The first supply duct 5 with thecorresponding outlet openings 6 for the premix fuel may be recognized,in a manner known from the prior art, on such an air inlet slot 4. Thesecond supply duct 7 with the corresponding second outlet openings 8 isarranged immediately adjacent to this first supply duct 5. The outletopenings 6, 8 of the two supply ducts point toward the inflowingcombustion air flow.

[0047] Due to the staging of the premix fuel quantities by means ofsupply ducts which can have mutually separate admission, the penetrationdepth of the premix fuel quantities P1, P2 into the combustion air flowcan be set to be large over one supply duct and to be small over theother supply duct. This is represented diagrammatically in FIG. 2, whichfigure represents the arrangement of FIG. 1 in a possible mode ofoperation. In this case, the fuel quantity in the first supply duct 5 isset to be higher than it is in the second supply duct 7, so that thepressure, and therefore the outlet velocity, of the fuel at the outletopenings 6 is increased as compared with the outlet openings 8. Thefirst premix fuel P1 from the first supply duct 5 therefore penetratesdeeper into the combustion air flow than the premix fuel P2 from thesecond supply duct 7, as is indicated in the figure. The same effect canalso be achieved by different opening diameters or flow cross sectionsof the respective outlet openings, it then being possible to select thefuel quantities flowing through the two ducts to be identical fordifferent penetration depths.

[0048] With this arrangement, therefore, the mixture distribution andthe mixing quality in the burner can be set in a specified manner.

[0049]FIG. 3 shows a variant of the arrangement of the supply ducts andthe outlet openings. In this example also, the conical swirl body 1 isrepresented with respectively first and second supply ducts 5, 7, instrongly simplified form for purposes of illustration. In this casealso, the two supply ducts are located in parallel adjacent to oneanother on the tangential air inlet slot—not represented. In thisarrangement, the two supply ducts have the same number of holes n1 andn2. The holes are uniformly distributed along the burner longitudinalaxis 3, the axial arrangement of the holes 8 of the second supply duct 7being set on gaps relative to the axial arrangement of the holes 6 ofthe first premix fuel supply conduit. The number of holes n1 and n2 canalso, of course, be different from one another.

[0050] The possibility of arranging or distributing the holes of thesupply ducts differently or to provide them with different diameterspermits the axial and radial fuel distribution in the burner and/or atthe burner outlet to be influenced in a specific manner.

[0051] As an example, the axial and radial fuel distribution can beinfluenced by a non-uniform arrangement of the holes 8 along the secondsupply duct 7 or the burner longitudinal axis 3, as is represented inthe following figures.

[0052] In these, FIG. 4 shows an arrangement in which the holes 6 of thefirst supply duct 5 are distributed in the usual manner at uniformdistances apart in the direction of the burner longitudinal axis 3. Inthis example, the holes 8 of the second supply duct 7 are onlydistributed in the direction of the burner longitudinal axis 3 over thefirst half of the swirl space. By means of this hole arrangement, anenrichment of the fuel mixture in the burner center can be achieved byswitching on this second stage—the premix fuel supply via the secondsupply conduit 7.

[0053]FIG. 5 shows a similar arrangement in which the holes 8 of thesecond supply duct are likewise arranged in the direction of the burnerlongitudinal axis 3 in the first region of the swirl space, as in thecase of FIG. 4. In this example, however, the holes 6 of the firstsupply duct 5 are not distributed over the complete length of the swirlspace in the direction of the burner longitudinal axis 3 but only in thesecond part, which is directed towards the burner outlet. The number n1or n2 of the respective holes can be selected to suit the requirements.These can be the same or can also be different.

[0054] A comparable design with interchanged arrangement of the outletholes 6, 8 in the direction of the burner longitudinal axis 1 [sic] isshown in FIGS. 6 and 7. In the arrangement of FIG. 6, in particular, theenrichment of the outer region of the burner, i.e. the region facingtowards the combustion chamber, can be achieved by means of the secondstage. Fundamentally, a desired concentration gradient of the fuel alongthe burner longitudinal axis can be set by means of arrangements such asare represented in FIGS. 4 to 7.

[0055] By means of an arrangement such as is represented in FIG. 4, itis also possible to supply pilot fuel at low loads. In this case,starting is carried out with the stage which injects the fuel into thecenter of the burner. With increasing load, the second stage is thenswitched on. At full load, for which as uniform as possible fueldistribution is desired, operation is then by means of the second stageonly.

[0056]FIG. 8 shows a further example of the embodiment of a burneraccording to the invention, in strongly diagrammatic representation. Inthis example, a purely cylindrical swirl body 1 is employed. The twosupply conduits 5, 7 indicated in the figure, with the first outletholes 6 and second outlet holes 8, can be designed and arranged in asimilar manner, as has already been explained in association with theprevious figures.

[0057] A further embodiment of a burner using, in this example, acylindrical swirl generator 1 with conical inner body 9 for carrying outthe present method is represented, as an example, in FIG. 9. In thiscase, FIG. 9 again shows the first supply duct 5 and the second supplyduct 7, with the corresponding outlet openings 6, 8. In the exemplaryembodiment of FIG. 9, these supply ducts are arranged adjacent to oneanother in the outer shell of the swirl body 1.

[0058]FIG. 10 shows an example of an embodiment of the burner accordingto the invention in which the second supply duct 7 is arranged on thecylindrical inner body 9.

[0059] In this arrangement, the second supply duct 7 is preferablyarranged within the outer wall of the inner body 9, a symmetricaldistribution of a plurality of supply ducts 7 around the burnerlongitudinal axis 3 being desirably selected in this case, as in thecase of the previous examples. In this example, however, it is alsopossible to let the second supply conduit 7 extend centrally within theinner body 9, it being then necessary to configure the outlet openings 8by means of corresponding ducts extending radially relative to the swirlspace 2. One or a plurality of additional outlet openings with acorrespondingly separated fuel supply (as pilot stage) or air can alsobe provided in the front, narrowing region of the inner body 9.

[0060] The FIGS. 11 to 14 show, diagrammatically, examples of furtherswirl generator geometries by means of which the present invention canbe effected. Represented from top to bottom in the figures are a burnerwith conical swirl body 1 and conical inner body 9, a burner with swirlbody 1 configured in the form of a reversed cone and conical inner body9, a burner with tulip-shaped swirl body 1 and a burner withfunnel-shaped swirl body 1. In all these burner geometries, the secondsupply conduits can be arranged both in the swirl body 1 and in theinner body 9, as in the previous examples. A common feature of all thegeometries shown here is the fact that the axial flow cross section ofthe swirl space increases toward the burner outlet in the region of theswirl body. Although this is not an absolutely necessary preconditionfor a premix burner of the generic type, it is an advantageousembodiment of the swirl generator.

[0061] In addition, all the burner geometries can be provided with apremixing tube 10, as is illustrated as an example in FIG. 15 for aconical burner and in FIG. 16 for a cylindrical burner with conicalinner body 9.

[0062] Finally, FIGS. 17 and 18 show, diagrammatically, two examples forthe construction of a swirl body, in cross section, such as can beemployed in the burner according to the invention. FIG. 17 represents aswirl body which is composed of four mutually offset shells 1 a, 1 b, 1c, 1 d which, in the arrangement represented, form four tangential airinlet slots 4. In the cross section shown, the shells can be formeddifferently, for example as circular-shaped segments, elliptical oroval. In the configuration represented, the partial bodies 1 a, 1 b, 1c, 1 d are arranged in such a way that their respective central axes 3a, 3 b, 3 c, 3 d are arranged offset relative to the actual burnerlongitudinal axis. The design of a burner, with or without mixing tube,with such a geometry can be taken in detail from EP 321 809 or EP0780629.

[0063]FIG. 18 represents a monolithic swirl body 1 with tangential airinlet openings 4 introduced into it. The air inlet openings 4 can, forexample, be configured as air inlet slots, which have been milled on, oras rows of air inlet holes.

[0064] The combinations of the supply ducts and the arrangement ordesign of the outlet openings in the supply ducts, as given in theprevious and following examples, can be arbitrarily altered or combinedwith one another. As an example, all the variants of the outlet openingarrangements represented in FIGS. 4 to 7 can also be used in the designsof FIGS. 8 to 16. This applies both to the distribution and number andto the arrangement of the individual outlet openings. Furthermore,different hole diameters can be employed in the two supply ducts in thecase of all the variants shown. In this way, a certain upstream pressureand a desired outlet velocity can be set in the stage which has toaccept a smaller fuel quantity. In this case, no limits are set to thecombination possibilities of the individual design variants. Thespecialist will select the corresponding arrangement to suit the desiredemployment condition and desired effects. In particular, it is by nomeans imperative to arrange the outlet openings equidistantly in theaxial direction, as is implicit in all the drawings. Quite on thecontrary, it can be found to be highly advantageous to arrange theoutlet openings for the premix fuel in an arbitrary axial distribution,or to implement other distribution rules, such as a geometrical stagingof the axial distances apart.

[0065] The same applies to the employment of different burner geometriesor the combination of swirl generators with inner bodies or premixingtubes. The specialist can see that it is possible to effect the presentinvention with different burner types and combinations of swirl bodies,inner bodies, premix tubes and other known features of burners.

[0066] Further very advantageous embodiments of a burner may berecognized in FIGS. 19 to 21. The burners represented comprise theconical swirl body 1, in whose outer shell are arranged, on the inletflow edges of the air inlet slots, a first group of outlet openings 6for premix gas. The burners are, furthermore, equipped with a centralfuel lance 12, which can have a nozzle at their combustion-chamber ends,i.e. at their tip—as in the present example—which nozzle can be used fora liquid fuel 13 or for a pilot fuel. Outlet openings for shroud air 14can be provided, in a known manner, around this nozzle. In addition tothe fuel supply conduits to the first group of outlet openings 6 and afuel supply conduit for injecting liquid fuel 13 at the tip of the fuellance 12, the burners represented have a further fuel supply conduit toa second group of outlet openings 8 in the fuel lance 12. The outletopenings 8 of the second group are essentially arranged in the outersurface of the fuel lance 12 in the direction of the burner longitudinalaxis, as may be seen in FIGS. 19 to 21, and are preferably distributedradially symmetrically about the longitudinal axis of the fuel lance 12.They permit the injection of fuel from the fuel lance 12 into the swirlspace in such a way that it is directed radially outward. The number andsize of these outlet openings 8 and their distribution on the fuel lance12—in the axial direction and peripheral direction—is [sic] selected asa function of the respective requirements of the burner, such asextinguishing limits, pulsations and flash-back limits.

[0067] The fuel lance 12 can extend relatively far into the swirl space(see FIGS. 19 and 20; “Long Lance EV Burner”) or, also, protrude only ashort distance into the swirl space (FIG. 21). In both cases, the secondgroup of outlet openings 8 is preferably arranged on the fuel lance 12in the rear region of the swirl space, i.e. in the region furthestremoved from the combustion chamber, as is indicated in the figures.

[0068] In these exemplary embodiments also, it is obviously possible tohave open-chain or closed-loop control of the fuel supply to the firstgroup of outlet openings 6 independently of the fuel supply to thesecond group of outlet openings 8.

[0069] The embodiment of FIG. 19 permits a very advantageous, stagedmode of operation of the burner, in which mode both the fuel supplyconduits to the first group of outlet openings 6 and the fuel supplyconduits to the second group of outlet openings 8 are fed with premixgas. The possibility of independently controlling the fuel supply to thefirst and second groups of outlet openings 6, 8 permits a mode ofoperation which is optimally matched to the respective operatingconditions of the burner or of the installation utilizing the burner. Inthis example, the second group of outlet openings 8 on the fuel lance 12are located opposite to the outlet openings of the first group of outletopenings 6 on the swirl body 1 so that, under certain operatingconditions, it is also possible to exclusively supply the first andsecond groups of outlet openings 6, 8 with fuel, i.e. without supplyingthe other respective group.

[0070] In principle, given corresponding supply of the fuel andcorresponding design of the second group of outlet openings, the burnerrepresented in the figure can also be operated in the diffusion mode bymeans of these outlet openings 8. Because of the spatial separation ofthe outlet openings 8 from the injection of liquid fuel 13 at the tip ofthe fuel lance 12, it is possible, in this case and in contrast to knownburners, to avoid the penetration of fuel droplets or of fuel vapor intothe fuel supply system for the second group of outlet openings 8.

[0071]FIG. 20 shows an embodiment of a burner which can likewise beoperated in the very advantageous staged mode of operation. The outletopenings 6 are closed or no outlet openings 6 are provided on theregions of the swirl body 1 opposite to the second group of outletopenings 8 because the function of these openings is taken over by theoutlet openings 8 on the fuel lance 12. FIG. 21 shows the same burnerwith shortened fuel lance 12, which burner is configured for the samemode of operation.

[0072] During the operation of these burners, premix gas is admitted toboth groups of outlet openings 6, 8. Ignition and starting of the burnertakes place in a mode of operation in which the premix gas is mainlyintroduced into the swirl space via the outlet openings 8 on the fuellance 12, also designated as stage 1 below. With increasing load, thesupply of the premix gas to Stage 1 is reduced and the supply of premixgas via the first group of outlet openings 6, designated as stage 2below, is increased. Such a distribution of the premix fuel between thestages 1 and 2 as a function of the operating condition of the burnercan be taken, as an example, from FIG. 22.

[0073] In this way, a gas turbine can, for example, be operated withsuch a burner from ignition to basic load without a pilot stage.

[0074] The supply of fuel to the stages 1 and 2 is controlled, in anopen-chain or closed-loop manner, by means of suitable valves.

[0075]FIGS. 23 and 24 show examples of the supply of a fuel quantity P0to the burner. In the case of both examples, the fuel line branches inorder to divide the total fuel quantity P0 between a fuel quantity P1for the first group of outlet openings 6 and a fuel quantity P2 for thesecond group of outlet openings 8.

[0076] In FIG. 23, the setting of the division ratio or mass flow ratiotakes place by means of one valve 15 or 16 in each of the branches. FIG.24 shows an embodiment in which the one valve 16 is arranged before thebranch for setting the total fuel quantity P0 and a further valve 15 isarranged in the branch for the first group of outlet openings 6. Bycontrolling the valve 15, it is possible to change the mass flow ratiobetween P1 and P2 in this case also. In this example, the valve 15 can,of course, also be arranged in the branch to the second group of outletopenings 8.

[0077] In addition, such an arrangement also permits a plurality ofburners to be simultaneously supplied with fuel at the mass flow ratioset, as is indicated by the dashed lines in the figures.

[0078] In both exemplary embodiments, the mass flow ratio P1/P2 ischanged by activating the valves as a function of the operatingcondition of the burner. The change to the mass flow ratio can becontrolled, in an open-chain or closed-loop manner, as a function ofdifferent measured and operating values, as has already been stated in aprevious part of the present description. The designs presented areindependent of the burner geometry and can be employed in all burners ofthe previous exemplary embodiments.

List of Designations

[0079]1 Swirl generator

[0080]1 a Swirl generator partial body

[0081]1 b Swirl generator partial body

[0082]1 c Swirl generator partial body

[0083]1 d d Swirl generator partial body

[0084]2 Swirl space

[0085]3 Burner longitudinal axis

[0086]3 a Longitudinal axis of a swirl generator partial body

[0087]3 b Longitudinal axis of a swirl generator partial body

[0088]3 c Longitudinal axis of a swirl generator partial body

[0089]3 d Longitudinal axis of a swirl generator partial body

[0090]4 Inlet openings/air slots

[0091]5 First fuel supply conduits

[0092]6 First fuel outlet openings

[0093]7 Second fuel supply conduits

[0094]8 Second fuel outlet openings

[0095]9 Inner body

[0096]10 Premix tube

[0097]11 Combustion air

[0098]12 Fuel lance

[0099]13 Liquid fuel

[0100]14 Shroud air

[0101]15 Control valve

[0102]16 Control valve

[0103] P0 Total fuel quantity

[0104] P1 First premix fuel

[0105] P2 Second premix fuel

[0106] n1 First number of holes

[0107] n2 Second number of holes

1. Method of operating a burner, said burner having a longitudinal axis,said burner comprising at least one first fuel supply conduit (5) with afirst group of fuel outlet openings (6), essentially arranged in thedirection of a burner longitudinal axis (3), for the introduction of afirst premix fuel quantity into a swirl space and one or a plurality ofsecond fuel supply conduits (7) with a second group of fuel outletopenings (8) essentially arranged in the direction of the burnerlongitudinal axis (3), it being possible to admit fuel to the secondfuel supply conduits (7) independently of the first fuel supply conduit(5), in which the supply of the fuel via the first fuel supply conduits(5) is open-chain controlled or closed-loop controlled separately fromthe supply of the fuel via the second fuel supply conduits (7),characterized in that the same fuel is supplied to the first and secondfuel supply conduits (5, 7).
 2. Method according to claim 1,characterized in that premix fuel is supplied to the first fuel supplyconduit or conduits (5) and the second fuel supply conduit or conduits(7).
 3. Method according to claim 1 or 2, characterized in that gaseousfuel is supplied to the first fuel supply conduit or conduits (5) andthe second fuel supply conduit or conduits (7).
 4. Method according toone of claims 1 to 3, characterized in that the fuel is introduced intothe burner in such a way that it is distributed between the first (5)and the second fuel supply conduits (7) as a function of the load. 5.Method according to one of claims 1 to 3, characterized in that the fuelis introduced into the burner in such a way that it is distributed, as afunction of the burner air/fuel ratio, between the first (5) and secondfuel supply conduits (7).
 6. Method according to one of claims 1 to 3,characterized in that in a first operating condition, the total fuelquantity is essentially supplied via the first fuel supply conduit orconduits (5) and is introduced into the combustion airflow via the firstgroup of fuel outlet openings (6), and in that, in a further operatingcondition, at least a part of the total fuel quantity is supplied to theburner via at least one of the second fuel supply conduits (7) with thesecond group of fuel supply openings (8).
 7. Method of operating aburner according to claims 1 to 3 in a heat generator, characterized inthat, in a partial load condition of the heat generator, the total fuelis supplied via the first fuel supply conduits (5), and in that, in atleast the full-load operation of the heat generator, the fuel is splitbetween the first fuel supply conduits (5) and at least one second fuelsupply conduits (7).
 8. Burner, consisting essentially of a swirlgenerator (1) for a combustion airflow (11), a swirl space (2) and meansfor introducing fuel into the combustion airflow, the swirl generator(1) having combustion air inlet openings (4) for the combustion airflowentering tangentially into the swirl space (2), which means includemeans for introducing fuel into the combustion airflow of at least onefirst fuel supply conduit (5) with a first group of fuel outlet openings(6), essentially arranged in the direction of a burner longitudinal axis(3), for a first premix fuel quantity (P1), and the burner has one or aplurality of second fuel supply conduits (7) with a second group of fueloutlet openings (8), essentially arranged in the direction of the burnerlongitudinal axis (3), for a second fuel quantity (P2), it beingpossible to admit fuel to these second fuel supply conduits (7)independently of the first fuel supply conduits (5), characterized inthat an inner body (9) is arranged in the swirl space (2), the fueloutlet openings (8) of at least one second fuel supply conduit (7) beingarranged on the inner body (9) in such a way that they are essentiallydistributed in the direction of the burner longitudinal axis (3). 9.Burner according to claim 8, characterized in that the inner body (9) isa fuel lance (12) which has, at its combustion-space end, at least oneoutlet nozzle for liquid fuel (13) and/or pilot fuel.
 10. Burneraccording to claim 8 or 9, characterized in that the fuel outletopenings (8), which are arranged in such a way that they are distributedon the inner body (9) in the direction of the burner longitudinal axis(3), are arranged in a partial axial region of the inner body (9) remotefrom the combustion-space end.
 11. Burner according to one of claims 8to 10, characterized in that the second group of fuel outlet openings(8) is designed for the supply of premix fuel.
 12. Burner according toone of claims 8 to 11, characterized in that at least one of the groupsof fuel outlet openings is arranged in the region of at least one of thefuel inlet openings (4).
 13. Burner according to one of claims 8 to 12,characterized in that a plurality of first fuel supply conduits (5) anda plurality of second fuel supply conduits (7) are provided, a secondfuel supply conduit (7) being associated with each of the first fuelsupply conduits (5).
 14. Burner according to one of claims 8 to 13,characterized in that second fuel supply conduits (7) are arrangedimmediately adjacent to first fuel supply conduits (5).
 15. Burneraccording to one of claims 8 to 14, characterized in that the fuel inletopenings (4) are tangential inlet slots extending essentially in thedirection of the burner longitudinal-axis (3).
 16. Burner according toclaim 15, characterized in that a first fuel supply conduit (5) with afirst group of fuel outlet openings (6) is arranged along each inletslot.
 17. Burner according to claim 15 or 16, characterized in that atleast one second fuel supply conduit (7) with a second group of fueloutlet openings (8) is arranged along each inlet slot.
 18. Burneraccording to one of claims 8 to 17, characterized in that the fueloutlet openings (8) of one or a plurality of second fuel supply conduits(7) are arranged at axial positions between the fuel outlet openings (6)of one or a plurality of first fuel supply conduits (5).
 19. Burneraccording to one of claims 8 to 18, characterized in that the fueloutlet openings (6, 8) of all groups are distributed over the whole ofthe axial extent of the combustion-air inlet openings (4).
 20. Burneraccording to one of claims 8 to 18, characterized in that the fueloutlet openings (6, 8) of at least one of the groups are distributedover the whole of the axial extent of the combustion-air inlet openings(4) and the fuel outlet openings (6, 8) of at least of one further groupare distributed over a partial axial region of the combustion-air inletopenings (4).
 21. Burner according to one of claims 8 to 18,characterized in that the fuel outlet openings (6, 8) of at least one ofthe groups are distributed over a first partial axial region of thecombustion-air inlet openings (4) and the fuel outlet openings (6, 8) ofother groups are distributed over further partial axial regions of thecombustion-air inlet openings (4).
 22. Burner according to claim 21,characterized in that the partial axial regions do not overlap. 23.Burner according to claim 21, characterized in that at least two of thepartial axial regions overlap at least partially.
 24. Burner accordingto one of claims 8 to 23, characterized in that the fuel outlet openings(6, 8) of two or more groups have different flow cross sections. 25.Burner according to one of claims 8 to 24, characterized in that meansare provided for the independent control of the premix fuel supply tothe first fuel supply conduit or conduits (5) and to the second fuelsupply conduit or conduits (7).
 26. Burner according to claim 25,characterized in that means for the independent control of the premixfuel supply have a common fuel line, which branches into a first supplyline to the first fuel supply conduit or conduits (5) and into a secondsupply line to the second fuel supply conduit or conduits (7), a valve(15, 16) for setting the fuel flow quantity being arranged in one of thesupply lines.
 27. Burner according to one of claims 8 to 26,characterized in that fuel can be admitted to a plurality of the secondfuel supply conduits (7) independently of one another.